310 



MISCELLANEOUS. 



Description of the Larva of a Brachiopod. 

 By F. Muller. 



Dr. F. Muller has sent from Brazil the description of a larva be- 

 longing undoubtedly to a Brachiopod, which is the more interesting 

 as the Brachiopoda are the only Mollusca regarding the development 

 of which we have no information. 



The larva in question is a small, perfectly orbicular bivalve Mol- 

 lusk. The two valves are similar, but unequal in size, the dorsal 

 valve being the largest. At the place of the hinge a small oval plate 

 is placed transversely between the two valves of the shell. The 

 mantle is gaping all round. Five pairs of very stiff setse, of which 

 one is much stronger than the others and curved backwards, project 

 at the periphery. They originate in the mantle of the ventral half; 

 at least, this is the case with four of them. A series of finer setae 

 spring from the circumference of the mantle of the dorsal valve, 

 and curve down upon the outside of the ventral valve. The animal, 

 as well as the shell, would be divided into two perfectly symmetrical 

 halves by a plane drawn vertically through the middle of the hinge. 

 The body, which is furnished with an alimentary canal, two auditory 

 capsules, and two eyes, fills the posterior half of the space between 

 the valves. The anterior half is occupied by four pairs of cylindrical 

 arms, between which a rounded knob is situated. Behind this knob 

 the mouth is perceptible. These four pairs of arms are supported 

 upon a common peduncle, at the extremity of which, therefore, the 

 mouth is placed. The arms are covered with a very well developed 

 ciliary coat, by the agency of which the little animal swims. The 

 reproductive and circulatory organs are wanting. 



During natation, the mouth is always directed forwards, which is 

 in favour of the generally received opinion as to the anterior and 

 posterior regions in the Brachiopoda. It is, in fact, now evident that 

 the Brachiopods are depressed animals, have an anterior or ventral 

 and a posterior or dorsal valve. MM. Agassiz and Vogt are there- 

 fore wrong in regarding them as compressed animals, like the Lamel- 

 libranchiate Mollusks — that is to say, as animals having a right and 

 a left valve. 



The larva, moreover, can not only swim, but also creep. This 

 latter mode of progression is effected by a sort of rotation of the ven- 

 tral valve alternately to the right and left. In this movement the 

 animal pushes by supporting itself principally upon the strongest of 

 the bristles above mentioned. — Reichert und Bu Bois' Archiv, 

 1860, p. 72. 



